The main focus of Josh Levin's article is a single day of brainstorming, led by GBN:

For nearly three hours, we run through America-killers that range from the believable to the science fiction-y: rising sea levels, a collapse of entitlement programs, an attack by a foreign power on American soil, a pandemic 10 times worse than the 1918 flu, global domination by a space-faring nation that uses geo-engineering to "turn off" climate change, and the emergence of a transnational class of biologically enhanced supermen and women... who identify more with one another than with any particular nation.

The article also heads off towards Robert Wright, Igor Panarin, and the Institute for the Future. The latter's Jamais Cascio gets his turn to describe several 50-year scenarios:

Cute note about futurism: "Most scenario-planning sessions end with the world stuffed inside a grid."